Electric furnace



Nov/29, 1927. f 1,650,658

-.|. A. SEEDE ELECTRIC FURNACE Filed June 5', 1926 Inventor; John A. Seeds,

Patented New: 29, 192

. UNITED STATES JOHN A. SEEIDE, OF

ELECTRIC Application filed June 5,

.1" bide, etc, and has forits object-the provision of simple and reliable control means whereby the electric heating current may be caused to pass either from one electrode to another or from one or more electrodes through the charge and the. furnace lining.

In carrying out my invention in one form as applied to a three-phase circuit, 1 provide three electrodes in the top of the furnace which are connected to the secondary terminals of 'a three-phase supply transformerand a fourth electrode embedded or otherwise connected in the bottom of the furnace'crucible and electrically connected to the neutral point of the transformer secondary. I also provide means for reversing the connections of one coil of the transformer primary winding so as to control current through the bottom electrode.

For a more complete understanding of my invention, reference should be had to the accompanying drawing, the single figure of which shows in somewhat diagrammatic fashion, an electric furnace embodying my invention.

Referring to the drawing, I have shown my invention in one form as applied to a smelting furnace, the furnace structure comprising a crucible made of a suitable heat refractory material, such as fire clay. This crucible as shown, is mounted in a jacket of heat refractory bricks 11. A pouring orifice 12 communicates with the bottom of the reservoir 13 for the charge 14. As shown, this orifice is plugged by means of a clay ball 12.

The charge is heated by means of three vertically arranged carbon electrodes 15, 16 and 17: which are suitably supported in a.

well known manner so as to hang downward into the reservoir 13 into electrically conducting or. arcing relation with the charge. These three electrodes are connected through a transformer 18 with a suitable three-phase alternating current supply source 19, the electrodes being connected directly to the terminals of the transformer secondary winding 20, which consists of three coils, 20 20 and 20 connected in star. A connection is also provided from a neutral point 21 of the secondary wind- PATENT OFFICE.

SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

FURNACE.

1926. Serial No. 114,010.

ing-through a conductor 22 to the bottom of the crucible 10'. As shown, this connec tion is made bymeans of a bottom electrode 23 which is embedded in the bottom wall of thecrucible 10 and connected with the con ductor 22. y

The primary winding 24 of thetrjahsformer has its coils connected in delta to the supply source 19. Theconnections for one of the primary windings, however, are such that they can be reversed. 'As shown, the primary winding 25 is connected to the supply source through a reversing switch 26. lVith the switch thrown downward to the position shown in the drawing, the primary coils are connected in delta and the secondary coils have the usual 120 three phase voltage relationship. By throwing the switch upward to its other position the connections for the winding 25 are reversed whereby the voltage of the coil 2O of the secondary winding is reversed so that this coil has a voltage phaserelation with respect to the voltages of the other two secondary coils 20 and 20.

In the operation of the furnace the switch 26 will normally be thrown to its lower position as shown in the drawing and under these conditions of operation no current will flow through the conductor 22 and the-bottom electrode 23 as long as the load between the three electrodes 15, 16 and 17 v is balanced.

With the heat for the furnace generated in this manner by the current passing between the three upper electrodes 15, '16 and 1?, it will be observed that the heat is generated at the top of the charge and consequently the temperature will be much higher at the top than at the bottom. Ordinarily, arcs will be formed between the upper electrodes and the charge, and the lengths of t e arcs will be varied as desired by adjust'ng the electrodes vertically so as to regulatev the rate of heat generation.

Under certain conditions it may be desired to raise the temperature of the bottom" of the charge. This may be necessary, for example, in case the molten product has solidified around the outlet orifice 12 so as to close it. In such case the switch 26 is thrown to its upper position a suitable time prior to the pouring of the product wheretrodes, the crucible l0 electrically conduct ing at the temperature involved, This current is substantially twice the current normally flowing in. each of the upper electrodes and the bottom of the crucible will be rapidly heated by reason of its own resistance and also the resistance of the charge to some extent. In this way any product clogging the pouring orifice will be melted out.

Vhile I have described my invention as embodiedin concrete form and as operating in a specific manner in accordance with the provisions of the Patent Statutes, it should 1 be understood that I do not limit my invention thereto since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is- 1. The combination with a metal melting furnace provided with a plurality of electrodes above the charge, a three phase source of electrical supply, transformer means comprising primary and secondary coils said secondary coils being star connected, connections between the terminals of said secondary coils and said upper electrodes, a connection between the neutral point of said secondary coils and the bottom of said 't'urnace, electrical connections hetweensaid primary coils and said supply source, and means ifor reversing the connections of one of said primary coils so as to reverse the polarity of one of said secondary coils.

2. The combination with a metal melting furnace provided with three upper electrodes and a bottom electrodc, a three phase source of supply, a three phase transformer having delta connected primary coils and star connected secondary coils, connections between the terminals of said secondary coils and said upper electrodes, a connection between the neutral. point of said secondary coils and said bottom electrode, electrical connections between the primary coils of said transformer and said snpplysO/llrCe, and means for reversing; the connections of one of said primary coils whereby a cur-rent is caused to flow through said bottom electrode.

In witness whereof, I have hereunto set my hand this 4th day of June, 1926.

JOHN A. SEEDE. 

